1. Field of the Invention
The present invention relates to a signal processing device and, more particularly, to a technique for detecting the zero run length of codes and decoding to perform an inverse zigzag transform.
2. Description of the Background Art
FIG. 11 is a block diagram of the background art illustrating a decoder means 299 for decoding information, given in the form of Huffman codes, into image data.
The decoder means 299 comprises a Huffman decoding portion 201, an inverse quantization portion 202, an inverse zigzag transform portion 203, an inverse-discrete cosine transform portion (referred to as an "IDCT portion" hereinafter) 206, a Huffman code table 3, and a quantization table 4.
The Huffman decoding portion 201 receives a Huffman code HC and decodes the Huffman code HC in conjunction with the Huffman code table 3 to sequentially output a zero run length ZRL and a non-zero effective coefficient NZ. The inverse quantization portion 202 determines inversely quantized data IQ from the zero run length ZRL and the effective coefficient NZ in conjunction with the quantization table 4. The inverse zigzag transform portion 203 receives the inversely quantized data IQ and outputs a DCT coefficient D.sub.3. The IDCT portion 206 receives and converts the DCT coefficient D.sub.3 into restored image data D.sub.4.
The inverse quantization portion 202 performs multiplication upon a quantization coefficient Qi given from the quantization table 4 to output the inversely quantized data IQ. Specifically, the inverse quantization portion 202 sequentially updates addresses of the quantization table 4 and multiplies the quantization coefficient Qi corresponding to an address by either the effective coefficient NZ or the value "0". Since no zero run length ZRL but only an effective coefficient NZ is first obtained from a block of Huffman codes, the quantization coefficient Qi corresponding to the first address is multiplied by the effective coefficient NZ. Thereafter, since a pair of zero run length ZRL and effective coefficient NZ are provided, the quantization coefficient Qi is multiplied by the value "0" as many times as the magnitude of the zero run length ZRL in succession, and then the quantization coefficient Qi is multiplied by the effective coefficient NZ.
The inverse zigzag transform portion 203 receives the inversely quantized data IQ and performs an inverse zigzag transform by arranging the inversely quantized data IQ in zigzag order and reading them in serial order, to output the DCT coefficient D.sub.3.
In the conventional decoder means 299, the number of multiplications in the inverse quantization portion 202 is required to correspond to a block of Huffman codes. For instance, when an image data corresponding to one block of Huffman codes includes 8.times.8=64 pixels, the inverse quantization portion 202 is required to perform sixty-four multiplications in corresponding relation to the one block of Huffman codes.
Similarly, the inverse zigzag transform portion 203 is required to arrange sixty-four data in zigzag form in corresponding relation to the one block of Huffman codes.
This results in time-consuming arithmetic operations and delayed processing times.